Re: [HACKERS] Block level parallel vacuum
От | Masahiko Sawada |
---|---|
Тема | Re: [HACKERS] Block level parallel vacuum |
Дата | |
Msg-id | CAD21AoAqT17QwKJ_sWOqRxNvg66wMw1oZZzf9Rt-E-zD+XOh_Q@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: [HACKERS] Block level parallel vacuum (Dilip Kumar <dilipbalaut@gmail.com>) |
Ответы |
Re: [HACKERS] Block level parallel vacuum
(Masahiko Sawada <sawada.mshk@gmail.com>)
Re: [HACKERS] Block level parallel vacuum (Mahendra Singh <mahi6run@gmail.com>) Re: [HACKERS] Block level parallel vacuum (Amit Kapila <amit.kapila16@gmail.com>) Re: [HACKERS] Block level parallel vacuum (Dilip Kumar <dilipbalaut@gmail.com>) Re: [HACKERS] Block level parallel vacuum (Mahendra Singh <mahi6run@gmail.com>) |
Список | pgsql-hackers |
On Mon, Oct 28, 2019 at 2:13 PM Dilip Kumar <dilipbalaut@gmail.com> wrote: > > On Thu, Oct 24, 2019 at 4:33 PM Dilip Kumar <dilipbalaut@gmail.com> wrote: > > > > On Thu, Oct 24, 2019 at 4:21 PM Amit Kapila <amit.kapila16@gmail.com> wrote: > > > > > > On Thu, Oct 24, 2019 at 11:51 AM Dilip Kumar <dilipbalaut@gmail.com> wrote: > > > > > > > > On Fri, Oct 18, 2019 at 12:18 PM Dilip Kumar <dilipbalaut@gmail.com> wrote: > > > > > > > > > > On Fri, Oct 18, 2019 at 11:25 AM Amit Kapila <amit.kapila16@gmail.com> wrote: > > > > > > > > > > > > I am thinking if we can write the patch for both the approaches (a. > > > > > > compute shared costs and try to delay based on that, b. try to divide > > > > > > the I/O cost among workers as described in the email above[1]) and do > > > > > > some tests to see the behavior of throttling, that might help us in > > > > > > deciding what is the best strategy to solve this problem, if any. > > > > > > What do you think? > > > > > > > > > > I agree with this idea. I can come up with a POC patch for approach > > > > > (b). Meanwhile, if someone is interested to quickly hack with the > > > > > approach (a) then we can do some testing and compare. Sawada-san, > > > > > by any chance will you be interested to write POC with approach (a)? > > > > > Otherwise, I will try to write it after finishing the first one > > > > > (approach b). > > > > > > > > > I have come up with the POC for approach (a). > > > > Can we compute the overall throttling (sleep time) in the operation > > > separately for heap and index, then divide the index's sleep_time with > > > a number of workers and add it to heap's sleep time? Then, it will be > > > a bit easier to compare the data between parallel and non-parallel > > > case. > I have come up with a patch to compute the total delay during the > vacuum. So the idea of computing the total cost delay is > > Total cost delay = Total dealy of heap scan + Total dealy of > index/worker; Patch is attached for the same. > > I have prepared this patch on the latest patch of the parallel > vacuum[1]. I have also rebased the patch for the approach [b] for > dividing the vacuum cost limit and done some testing for computing the > I/O throttling. Attached patches 0001-POC-compute-total-cost-delay > and 0002-POC-divide-vacuum-cost-limit can be applied on top of > v31-0005-Add-paralell-P-option-to-vacuumdb-command.patch. I haven't > rebased on top of v31-0006, because v31-0006 is implementing the I/O > throttling with one approach and 0002-POC-divide-vacuum-cost-limit is > doing the same with another approach. But, > 0001-POC-compute-total-cost-delay can be applied on top of v31-0006 as > well (just 1-2 lines conflict). > > Testing: I have performed 2 tests, one with the same size indexes and > second with the different size indexes and measured total I/O delay > with the attached patch. > > Setup: > VacuumCostDelay=10ms > VacuumCostLimit=2000 > > Test1 (Same size index): > create table test(a int, b varchar, c varchar); > create index idx1 on test(a); > create index idx2 on test(b); > create index idx3 on test(c); > insert into test select i, repeat('a',30)||i, repeat('a',20)||i from > generate_series(1,500000) as i; > delete from test where a < 200000; > > Vacuum (Head) Parallel Vacuum > Vacuum Cost Divide Patch > Total Delay 1784 (ms) 1398(ms) > 1938(ms) > > > Test2 (Variable size dead tuple in index) > create table test(a int, b varchar, c varchar); > create index idx1 on test(a); > create index idx2 on test(b) where a > 100000; > create index idx3 on test(c) where a > 150000; > > insert into test select i, repeat('a',30)||i, repeat('a',20)||i from > generate_series(1,500000) as i; > delete from test where a < 200000; > > Vacuum (Head) Parallel Vacuum > Vacuum Cost Divide Patch > Total Delay 1438 (ms) 1029(ms) > 1529(ms) > > > Conclusion: > 1. The tests prove that the total I/O delay is significantly less with > the parallel vacuum. > 2. With the vacuum cost divide the problem is solved but the delay bit > more compared to the non-parallel version. The reason could be the > problem discussed at[2], but it needs further investigation. > > Next, I will test with the v31-0006 (shared vacuum cost) patch. I > will also try to test different types of indexes. > Thank you for testing! I realized that v31-0006 patch doesn't work fine so I've attached the updated version patch that also incorporated some comments I got so far. Sorry for the inconvenience. I'll apply your 0001 patch and also test the total delay time. Regards, -- Masahiko Sawada
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